The present invention relates generally to gas turbine engines, and, more specifically, to reduction of exhaust noise and infrared (IR) signature.
A typical gas turbine engine includes a compressor for compressing air which is mixed with fuel and ignited in a combustor for generating hot combustion gases which flow through one or more stages of turbines which power the compressor in a core engine configuration. Typically cooperating with the core engine is a low pressure compressor, such as a fan, disposed upstream of the high pressure compressor of the core engine, which is operatively joined to a low pressure turbine disposed downstream from the high pressure turbine of the core engine. The combustion exhaust gases discharged from the core engine flow through the low pressure turbine which extracts energy therefrom for powering the low pressure compressor or fan for use in powering an aircraft in flight for example. Alternatively, the low pressure turbine may be used for producing output shaft power in a marine or land-based industrial (Mandl) application.
In a typical turbofan aircraft gas turbine engine application for powering an aircraft in flight, a core exhaust nozzle is used for independently discharging the core exhaust gases inwardly from a concentric fan exhaust nozzle which discharges the fan air therefrom for producing thrust. The separate exhausts from the core nozzle and the fan nozzle are high velocity jets typically having maximum velocity during take-off operation of the aircraft with the engine operated under relatively high power. The high velocity jets interact with each other as well as with the ambient air and produce substantial noise along the take-off path of the aircraft. Furthermore, the core jet is hot and produces an infrared signature which may be detected from afar.
The prior art includes various solutions for reducing jet noise and infrared signature. The solutions typically rely on vigorously mixing the hot core jet with the fan jet, or ambient air, or both, for reducing the velocities thereof and reducing the temperature thereof. In this way both noise and infrared signature may be reduced, but typically at the expense of engine efficiency and performance.
For example, convoluted or lobed mixers, also known as daisy mixers, may be used at the end of the core engine inside a long duct outer nacelle for internally mixing the core exhaust with the fan exhaust. Although noise and IR signature may be reduced, this is done at the expense of increases in nozzle weight, installed friction, and boat-tail drag. And, although jet noise may be reduced at lower frequencies, this is typically accompanied by an increased noise level at mid and high frequency ranges.
The mixer lobes are effective since they project into both the core exhaust and the fan exhaust, but therefore have performance losses associated therewith. Other types of sound suppressors are known which also project into the jet streams with differing degrees of performance loss and noise reduction. Exemplary devices include paddles, corrugations, mini-mixers, tabs, and vortex generators.
Accordingly, it is desired to reduce jet noise and IR signature with minimum reduction in engine performance, reduced mechanical complexity, and minimum increase, or even reduced, nozzle weight.
A gas turbine engine exhaust nozzle includes an exhaust duct for channeling a gas jet. A plurality of adjoining chevrons are disposed at an aft end of the duct to define an exhaust outlet. Each of the chevrons is triangular in configuration, with a base, apex, side trailing edges converging therebetween, and radially opposite first and second surfaces bounded thereby. The trailing edges of adjacent chevrons are spaced laterally apart to define respective diverging slots disposed in flow communication with the duct. The chevrons have a concave contour axially between the bases and apexes which promotes jet mixing through the slots.